British politics has taken another surprise turn after former Conservative leadership favourite Boris Johnson ruled himself out of the contest. The move comes after justice secretary Michael Gove, a fellow Vote Leave campaigner, made a surprise bid to become David Cameron's successor as prime minister.

Johnson, a former Mayor of London, was expected to go head-to-head with Home Secretary Theresa May in the leadership race. But he told a London audience on 30 June: "Having consulted my colleagues in view of circumstances in Parliament, I have concluded that the person [to become prime minister] cannot be me."

The surprising move will be a boost for Gove, who is now the leading Brexit backer in the Conservative leadership race. Stephen Crabb, the Work and Pensions Secretary, Andrea Leadsom, the Eurosceptic former city minister, and Dr Liam Fox, the former defence secretary, have also thrown their names into the hat.

May, who has been Home Secretary since 2010, mocked Johnson this morning (30 June): "The last time Boris Johnson did a deal with the Germans he came back with three nearly new water cannons."

Meanwhile, Gove claimed Johnson "cannot provide the leadership or build the team for the task ahead". He said: "I have repeatedly said that I do not want to be prime minister. That has always been my view. But events since last Thursday have weighed heavily with me.

"I respect and admire all the candidates running for the leadership. In particular, I wanted to help build a team behind Boris Johnson so that a politician who argued for leaving the European Union could lead us to a better future. But I have come, reluctantly, to the conclusion that Boris cannot provide the leadership or build the team for the task ahead.

"I have, therefore, decided to put my name forward for the leadership. I want there to be an open and positive debate about the path the country will now take. Whatever the verdict of that debate I will respect it."

As there are more than two candidates, Conservative MPs will vote them down in consecutive rounds. The two candidates will then face off in a vote by the party membership of more than 150,000.